Owing to progress in information communication networks such as Internet in recent years, users can easily access network information through personal terminals employing cellular phones or the like.
In such information communication, information is transmitted as digital signals. Therefore, each user can copy music data and video data, which are transmitted via the information communication network, without degradation in the audio quality and picture quality.
Accordingly, the right of the copyright owner may be significantly infringed when copyrighted content data such as music information and image data are transmitted over the information communication network without appropriate measures for protecting the copyrights.
Conversely, top priority may be given to the copyright protection by disabling or inhibiting distribution of content data over the digital information communication network, which is growing exponentially. However, this causes disadvantages to the copyright owner who can essentially collect a predetermined copyright royalty for data copying.
Instead of the distribution over the digital information communication network described above, distribution may be performed via record mediums storing digital data. In connection with the latter case, music data stored in CDs (Compact Disks) on the market can be freely copied in principle onto magneto-optical disks (e.g., MDs) as long as the copied music is only for the personal use. However, a personal user performing digital recording or the like indirectly pays predetermined amounts in prices of the digital recording device itself and the mediums such as MDs as guaranty moneys to a copyright owner.
Further, the music data is digital data formed of digital signals, and substantially no deterioration occurs in copied information when music data is copied from a CD to an MD. Therefore, for the copyright protection, such structures are employed that the music information cannot be copied as digital data from the recordable MD to another MD.
In view of the above, it is necessary to inhibit unauthorized further duplication of the received content data, which was distributed to the public over the information communication network.